The crystallization temperature estimated by the two. American mineralogist, volume 89, pages 14961504, 2004 new developments in twofeldspar thermometry a. For example, calcite caco 3 is soluble in acidic solutions. In this paper, we report the application of the modified two feldspar. Most of the nonclay components are identifiable in thin section, but clay minerals are so small feldspar modeling and thermometry mrnr. Assrracr a revised thermodynamic model for ternary feldspars an extension of the approach of.
Recent improvements in the experimental and thermodynamic basis of twofeldspar geothermometry allow one to recover temperatures of coexistence more reliably. The present plagioclase thermometry gives 167 degrees lower. Most ternary feldspars have negative excess volumesan important constraint on pressure corrections in geothermometry. A practical twofeldspar geothermometer geoscienceworld.
The exact composition of the various feldspar minerals depends on what elements balance the oxygen, which has two bonds to fill remember h 2 o. Ternaryfeldspar modeling and thermometry mineralogical society. Mineral chemistry perspective of nain ophiolite melange. The thermodynamic model of the twofeldspar thermometer has been revised. New developments in twofeldspar thermometry kielprints. Feldspar thermometry in ultrahightemperature metamorphic. The compositions of experimental products were determined using the electron microprobe. The bar at the lower right is 100 g and coarse exsolution of albite in alkali feldspar are common. Pdf ternary feldspar experiments and thermodynamic models. Will not go into details here, just note the existance of complexity associated with cation ordering and variations in structural characteristics. Mineral zoning, p t x m phase relations, and metamorphic.
For example, feldspar is altered by hydrolysis to clay minerals. The two types of feldspar are soda feldspar 7 percent or higher na o and potash feldspar 8 percent or higher k o. Gsa data repository 2015242 geological society of america. Two feldspar geothermometry is applied to granulite and amphibolitefacies feldspars from sri lanka.
Nov 29, 2019 temperatures of crystallization for all or portions of three thin granitic pegmatite dikes in southern california are derived from feldspar solvus thermometry, with supporting data from the kcs ratio of k feldspar, the extent of alsi order in k feldspar, and the texture of granophyre found along the margins of dikes. Amphibole thermometric data mantle pegmatite dyke and sheeted dyke gave a temperature. Njaud,e aberkeley geochronology center, 2455 ridge road, berkeley, ca 94709, usa bdepartment of earth and planetary science, university. Ternary feldspar thermometry of paleoproterozoic granulites. Is twofeldspar thermometry reliable for intrusive igneous rocks.
Twofeldspar thermometry can be applied, even where only one feldspar has preserved its original bulkcomposition in terms of alsi content, in spite of or because of unmixing to perthite or antiperthite. Albite or sodium feldspar is soluble in both orthoclase and anor thite. Retention of inherited ar by alkali feldspar xenocrysts in a. A geothermometer based on the partitioning of the albite component between plagioclase and alkali feldspar, such as the barth thermometer, is of great practical. Feldspar thermometry in ultrahightemperature metamorphic rocks. On the one hand, some minerals become altered to other minerals. In the great majority of pegmatite bodies there is no regularity whatsoever in the distribution of the different minerals. For feldspars monocrystals thermometry, several calibrations are available ex. Bohlen sr, essene ej 1977 feldspar and oxide thermometry of granulites in.
Timescales of mixing and mobilisation in the bishop tuff. Pyroxene thermometry yielded and estimated temperature which varied between 1100 c and 0 c figure 6 a for the different rock units of nom25. Much of the material mined as spar is coarsegrained graphic granite containing from 10 to 20 per cent of free quartz. Sep 15, 2012 40 ar 39 ar dating of volcanic alkali feldspars provides critical age constraints on many geological phenomena.
The spinel granulite data are based on gasparik 1984, 1985 adjusted to twopyroxene temperatures. Phase equilibria are from a twopyroxene granulite studied by irving 1974. Two feldspar thermometry 32 suggests initial temperatures of 820c at assumed midcrustal pressures of 0. This thermometer is more useful than previous two feldspar thermometers because it 1 fully accounts for ternary solid solution, 2 indicates whether the two feldspars could have been in equilibrium, and 3 gives further information about how the feldspar compositions may have been changed by such postcrystallization processes as alkali. Calorimetric investigation of the excess entropy of mixing in analbitesanidine solid solutions.
This thermometer is more useful than previous twofeldspar thermometers because it 1 fully accounts for ternary solid solution, 2 indicates whether the two feldspars could have been in equilibrium, and 3 gives further information about how the feldspar compositions may have been changed by such postcrystallization processes as alkali. The feldspars derive from different geological units, from different rocks involved in different acts of deformation and to feldspars which grew at. New developments in twofeldspar thermometry request pdf. Retention of inherited ar by alkali feldspar xenocrysts in. Status of thermobarometry in granitic batholiths earth and.
In plagioclases, are ordering two elements whose behavior must be coupled via charge compensation nasi caal. Feldspar thermometry in uht metamorphic rock 933 analytical stitute of polar research. Status of thermobarometry in granitic batholiths earth. Application of the twofeldspar geothermometer to ultrahigh. In glassmaking, alumina from feldspar improves product hardness, durability, and resistance to chemical corrosion. Entropy parameters have been fitted to the phase equilibrium data of seck 1971 and elkins and grove 1990.
In subsolvus or two feldspar granites crystallisation occurs at high water pressures resulting in the formation of two types of feldspar as opposed to hypersolvus granites in which crystallization at relatively low water pressures results in the formation of a single feldspar variety. Feldspar is a common raw material used in glassmaking, ceramics, and to some extent as a filler and extender in paint, plastics, and rubber. Feldspar thermometry can be applied either to pair minerals such as plagioclase and k feldspar or to hypersolvus feldspar monocrystals. Lattice strain across nak interdiffusion fronts in alkali.
Lindsley 1988, based on the experimental data by seck. Fuhrman and lindsley, 1988, elkins and grove, 1990 on solvcalc software wen and nekvasil, 1994 that allow calculations of. Temperatures of crystallization for all or portions of three thin granitic pegmatite dikes in southern california are derived from feldspar solvus thermometry, with supporting data from the kcs ratio of kfeldspar, the extent of alsi order in kfeldspar, and the texture of granophyre found along the margins of dikes. Most of the nonclay components are identifiable in thin section, but clay minerals are so small feldspar barometry open circles used harley 1984. Twofeldspar geothermometers are based on the tempera ture dependence of the solvus composition between coexisting alkali feldspar and plagioclase.
Models of ternary feldspars seck 1971a neues jahrb mineral. Pdf application of the twofeldspar geothermometer to ultrahigh. May contain very minor amount of oh groups, considered as defects e. Combined with ar diffusion kinetics for alkali feldspars and magma temperature inferred from two feldspar thermometry, the results indicate that 1% inherited 40ar can be retained in such xenocrysts despite immersion in magma at 900c for tens to 100 years. The thermodynamic model of the two feldspar thermometer has been revised. A procedure is suggested to correct for compositional changes due to retrograde resetting. In petrology the group is split into two major groups. Exsolved ilmenite ilm granulemagnetite m intergrowth. I was able to use two feldspar thermometers when studying contact melting. Feldspar and oxide thermometry of granulites in the.
Three of the samples come from areas of growth processes, or whether zoning has been subbelow the 725c isotherm et10, ph4, as19e, three stantially modi. We present twofeldspar thermometry and diffusion chronometry from sanidine, orthopyroxene and quartz from multiple samples of the bishop tuff, california, to constrain the temperature stratification within the preeruptive magma body and the. We present two feldspar thermometry and diffusion chronometry from sanidine, orthopyroxene and quartz from multiple samples of the bishop tuff, california, to constrain the temperature stratification within the preeruptive magma body and the. The feldspar was retrieved by dissolving the salt with deionised water at room temperature.
Experiments were carried out over the range 700 to 900 c and i to 3 kbar under watersaturated conditions. Pdf ternary feldspar experiments and thermodynamic. Although kfeldspars become perthitic and increasingly ordered toward the. Crystallization temperature determination of itokawa. Temperatures of crystallization for all or portions of three thin granitic pegmatite dikes in southern california are derived from feldspar solvus thermometry, with supporting data from the kcs ratio of k feldspar, the extent of alsi order in k feldspar, and the texture of granophyre found along the margins of dikes. Twofeldspar geothermometry is applied to granulite and amphibolitefacies feldspars from sri lanka. Lecture notes feldspars if quantity is of any significance, the feldspar minerals are the most important minerals for geologists studying the crust of the earth. Alkali feldspar feldspar minerals rich in sodium or potassium. Models of ternary feldspars seck 1971a neues jahrb. Elkins and grove 1990 new experimental data on coexisting ternary feldspars and a model for excess free energy that uses the simpler xlnx formulation for t. Retention of inherited ar by alkali feldspar xenocrysts in a magma. Oct 24, 20 the crystallization temperature of the particle ra.
From recent enthalpy and volume measurements in the na,ca. Assrracr a revised thermodynamic model for ternary feldsparsan extension of the approach of. This assumption is shown to fail dramatically in the case of a phonolitic lava from southern tanzania that. The activity expressions of this model permit yet another formulation of the two feldspar geothermometer that fully takes ternary solution into account. Pdf the paleoproterozoic khondalite belt in the north china craton preserves. Although k feldspars become perthitic and increasingly ordered toward the. Different methods of integration of the unmixed feldspars to get the original bulkcomposition are evaluated. Base on two feldspar thermometry and hornblendeplagioclase thermometry barometry, igneous temperatures of 750 to 770 o c and pressures of 4. Sanidine and orthoclase are monoclinic or nearly so.
The international organization for standardization has issued a set of norms related to thermometry, the basic one being iso 800005. The crystals were subsequently cut in two mutually perpendicular directions normal to the polished surface fig. Two feldspar thermometry can be applied, even where only one feldspar has preserved its original bulkcomposition in terms of alsi content, in spite of or because of unmixing to perthite or antiperthite. A key assumption is that alkali feldspar phenocrysts in magmas contain no initial radiogenic 40 ar 40 ar. In the hypersolvus rocks all the soda feldspar is or was in solid solution in the potash feldspar whereas in the subsolvus rocks the plagioclase is present as discrete grains. Feldspar thermometry can be applied either to pair minerals such as plagioclase and kfeldspar or to hypersolvus feldspar monocrystals. Thus, the probability distribution function for each modeled profile, and therefore the uncertainties given with the best fit ages illustrated in figure 3 of the main text include the propagated uncertainty from the mineral thermometry. This paper reports the results of 20 experiments in which mixes of two or three feldspars were reacted to produce coexisting plagioclase feldspar pf and alkali feldspar af. From recent enthalpy and volume measurements in the na,ca and k,ca feldspar binaries, new interaction parameters have been derived and previous ones have been updated.
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